/**************************************************************************************************
 * copyright: Copyright (c) 2007-2008 Diggory Hardy.
 *
 * author: Diggory Hardy, diggory.hardy@gmail.com
 *
 * license: BSD style: $(LICENSE)
 *
 * This contains templates for converting various data-types to a char[].
 *
 * parseFrom is roughly the inverse of $(B parseTo).
 * It is also available in tango.scrapple.
 *
 * This module basically implements the following templated function for most basic D types:
 * bool, byte, short, int, long, ubyte, ushort, uint, ulong, float, double, real, char, wchar,
 * dchar.
 * It also supports arrays of any supported type (including of other arrays) and has special
 * handling for strings (char[]) and binary (ubyte[]) data-types.
 * -----------------------------
 * char[] parseFrom(T) (T value);
 * -----------------------------
 *
 * $(I value) is the value to convert; it is converted to a string and returned.
 *
 * Syntax:
 * The syntax is the same as parseTo; but since this module only generates formatted output
 * knowing the syntax shouldn't be necessary. There is currently no way to specify options like
 * output base for ints, precision of floats, or
 * whether to write char[] or ubyte[] types as arrays or in their more compact forms.
 *
 * Throws:
 * On errors, an exception is thrown (UnicodeException or IllegalArgumentException). No other
 * exceptions should be thrown.
 *
 * Remarks:
 * There is currently no support for outputting wchar/dchar strings. There are, however, unicode
 * conversions for converting UTF-16/32 to UTF-8. Be warned though that many wchar/dchar characters
 * (any that are non-ascii) will not fit in a single char and an exception will be thrown.
 *
 * The code does involve some heap activity; this is necessary anyway for returning dynamic arrays.
 * (Slices of a pre-allocated array could be returned instead, but for many uses would have to be
 * duplicated before storage, leading to less efficient operation.)
 * Most memory allocation has been kept to a minimum.
 *
 * Unlike the parseTo!() module, the parseFrom templates could be re-written to use static-ifs
 * instead of type specialisation, thus allowing type inference. However I likely won't bother
 * implementing this myself.
 *
 * Examples:
 * ------------------------------------------------------------------------------------------------
 * // Examples are printed via Cout.
 *
 * // Basic examples:
 * Cout (parseFrom!(byte) (-13)).newline;                       // -13
 * Cout (parseFrom!(real) (2.56e11)).newline;                   // 2.55999999999999990000e+11
 * Cout (parseFrom!(double[]) ([0.0, 1.0, 2.0, 3.0])).newline;  // [0.00000000000000000,1.00000000000000000,2.00000000000000000,3.00000000000000000]
 * Cout (parseFrom!(bool[]) ([true,false,false])).newline;      // [true,false,false]
 *
 * // String and ubyte[] special syntaxes (always used):
 * Cout (parseFrom!(char[]) ("A string.")).newline;             // "A string." (including quotes)
 * Cout (parseFrom!(ubyte[]) (cast(ubyte[]) [5u, 0xF1u, 0x10u])).newline;   // 0x05f110
 *
 * // Associative arrays:
 * Cout (parseFrom!(char[][byte]) ([-1:"negative one"[], 0:"zero", 1:"one"])).newline;  // [0:"zero",1:"one",-1:"negative one"]
 *
 * // No limit on complexity...
 * char[] somethingComplicated = parseFrom!(real[][][bool[int[][]]]) (...);
 * ------------------------------------------------------------------------------------------------
 *************************************************************************************************/

module mde.mergetag.parse.parseFrom;

// tango imports
import tango.core.Exception : UnicodeException, IllegalArgumentException;
import cInt = tango.text.convert.Integer;
import cFloat = tango.text.convert.Float;
import Utf = tango.text.convert.Utf;
import Util = tango.text.Util;

//BEGIN parseFrom templates
/* Idea: could extend parseFrom with a second parameter, containing flags for things like base to output.
 * Unnecessary for mergetag though.
*/

// Associative arrays

char[] parseFrom(T : T[S], S) (T[S] val) {
    char[] ret;
    // A guess, including values themselves and [,:] elements (must be at least 2).
    ret.length = val.length * (defLength!(T) + defLength!(S) + 2) + 2;
    ret[0] = '[';
    uint i = 1;
    foreach (S k, T v; val) {
        char[] s = parseFrom!(S) (k) ~ ":" ~ parseFrom!(T) (v);
        i += s.length;
        if (i+1 >= ret.length) ret.length = ret.length * 2;	// check.
        ret[i-s.length .. i] = s;
        ret[i++] = ',';
    }
    if (i == 1) ++i;	// special case - not overwriting a comma
    ret[i-1] = ']';	// replaces last comma
    return ret[0..i];
}
debug (UnitTest) unittest {
    char[] X = parseFrom!(char[][char]) (['a':cast(char[])"animal", 'b':['b','u','s']]);
    char[] Y = `['a':"animal",'b':"bus"]`;
    assert (X == Y);
}


// Arrays

char[] parseFrom(T : T[]) (T[] val) {
    char[] ret;
    // A guess, including commas and brackets (must be at least 2)
    ret.length = val.length * (defLength!(T) + 1) + 2;
    ret[0] = '[';
    uint i = 1;
    foreach (T x; val) {
        char[] s = parseFrom!(T) (x);
        i += s.length;
        if (i+1 >= ret.length) ret.length = ret.length * 2;	// check length
        ret[i-s.length .. i] = s;
        ret[i++] = ',';
    }
    if (i == 1) ++i;	// special case - not overwriting a comma
    ret[i-1] = ']';	// replaces last comma
    return ret[0..i];
}

// Strings (array special case)
char[] parseFrom(T : char[]) (T val) {
    char[] ret = new char[val.length * 2 + 2];	// Initial storage. This should ALWAYS be enough.
    ret[0] = '"';
    uint i = 1;
    for (uint t = 0; t < val.length;) {
        // process a block of non-escapable characters
        uint s = t;
        while (t < val.length && !isEscapableChar(val[t]))
            ++t;	// skip all non-escapable chars
        uint j = i + t - s;
        ret[i..j] = val[s..t];	// copy a block
        i = j;
        // process a block of escapable charaters
        while (t < val.length && isEscapableChar(val[t])) {
            ret[i++] = '\\';				// backslash; increment i
            ret[i++] = replaceEscapableChar(val[t++]);	// character; increment i and t
        }
    }
    ret[i++] = '"';
    return ret[0..i];
}
// Unicode conversions for strings:
char[] parseFrom(T : dchar[]) (T val) {
    // May throw a UnicodeException; don't bother catching and rethrowing:
    return parseFrom!(char[]) (Utf.toString (val));
}
char[] parseFrom(T : wchar[]) (T val) {
    // May throw a UnicodeException; don't bother catching and rethrowing:
    return parseFrom!(char[]) (Utf.toString (val));
}

// Binary (array special case)
char[] parseFrom(T : ubyte[]) (T val) {
    static const char[16] digits = "0123456789abcdef";
    
    char[] ret = new char[val.length * 2 + 2];	// exact length
    ret[0..2] = "0x";
    uint i = 2;
    
    foreach (ubyte x; val) {
        ret[i++] = digits[x >> 4];
        ret[i++] = digits[x & 0x0F];
    }
    return ret;
}

debug (UnitTest) unittest {
    // generic array stuff:
    assert (parseFrom!(double[]) ([1.0, 1.0e-10]) == `[1.00000000000000000,0.10000000000000000e-09]`);
    assert (parseFrom!(double[]) (cast(double[]) []) == `[]`);		// empty array
    
    // char[] conversions, with commas, escape sequences and multichar UTF8 characters:
    assert (parseFrom!(char[][]) ([ ".\""[], [',','\''] ,"!\b€" ]) == `[".\"",",\'","!\b€"]`);
    
    // wchar[] and dchar[] conversions:
    // The characters were pretty-much pulled at random from unicode tables.
    // The last few cause some wierd (display only) effects in my editor.
    assert (parseFrom!(wchar[]) ("Test string: ¶α؟अกሀ搀"w) == "\"Test string: ¶α؟अกሀ搀\"");
    assert (parseFrom!(dchar[]) ("Test string: ¶α؟अกሀ搀"d) == "\"Test string: ¶α؟अกሀ搀\"");
    
    assert (parseFrom!(ubyte[]) (cast(ubyte[]) [0x01, 0xF2, 0xAC]) == `0x01f2ac`);	// ubyte[] special notation
}


// Basic types

// Char
char[] parseFrom(T : char) (T val) {
    // NOTE: if (val > 127) "is invalid UTF-8 single char"
    // However we don't know what this is for, in particular if it will be recombined with other chars later
    
    // Can't return reference to static array; making dynamic is cheaper than copying.
    char[] ret = new char[4];	// max length for an escaped char
    ret[0] = '\'';
    
    if (!isEscapableChar (val)) {
        ret[1] = val;
        ret[2] = '\'';
        return ret[0..3];
    } else {
        ret[1] = '\\';
        ret[2] = replaceEscapableChar (val);
        ret[3] = '\'';
        return ret;
    }
    assert (false);
}
// Basic unicode convertions for wide-chars.
// NOTE: any other wide-chars will not fit in a single UTF-8 encoded char.
const char[] WIDE_CHAR_ERROR = "Error: unicode non-ascii character cannot be converted to a single UTF-8 char";
char[] parseFrom(T : wchar) (T val) {
    if (val <= 127u) return parseFrom!(char) (cast(char) val);	// this char can be converted
    else throw new UnicodeException (WIDE_CHAR_ERROR, 0);
}
char[] parseFrom(T : dchar) (T val) {
    if (val <= 127u) return parseFrom!(char) (cast(char) val);	// this char can be converted
    else throw new UnicodeException (WIDE_CHAR_ERROR, 0);
}
debug (UnitTest) unittest {
    assert (parseFrom!(char) ('\'') == "\'\\\'\'");
    assert (parseFrom!(wchar) ('X') == "'X'");
    assert (parseFrom!(dchar) ('X') == "'X'");
}

// Bool
char[] parseFrom(T : bool) (T val) {
    if (val) return "true";
    else return "false";
}
// too simple to need a unittest

// Signed ints
char[] parseFrom(T : byte) (T val) {
    return formatLong (val);
}
char[] parseFrom(T : short) (T val) {
    return formatLong (val);
}
char[] parseFrom(T : int) (T val) {
    return formatLong (val);
}
char[] parseFrom(T : long) (T val) {
    return formatLong (val);
}
// Unsigned ints
char[] parseFrom(T : ubyte) (T val) {
    return formatLong (val);
}
char[] parseFrom(T : ushort) (T val) {
    return formatLong (val);
}
char[] parseFrom(T : uint) (T val) {
    return formatLong (val);
}
char[] parseFrom(T : ulong) (T val) {
    if (val > cast(ulong) long.max)
        throw new IllegalArgumentException ("No handling available for ulong where value > long.max");
    return formatLong (val);
}
debug (UnitTest) unittest {
    assert (parseFrom!(byte) (cast(byte) -5) == "-5");
    // annoyingly, octal syntax differs from D (blame tango):
    assert (parseFrom!(uint[]) ([0b0100u,0724,0xFa59c,0xFFFFFFFF,0]) == "[4,468,1025436,4294967295,0]");
}

// Floats
/* Old calculation (not used):
t.dig+2+4+3	// should be sufficient length (mant + (neg, dot, e, exp neg) + exp (3,4,5 for float,double,real resp.)) */
char[] parseFrom(T : float) (T val) {
    char[] ret = new char[32];	// minimum allowed by assert in format
    return cFloat.format (ret, val, T.dig+2, 1);	// from old C++ tests, T.dig+2 gives best(?) accuracy
}
char[] parseFrom(T : double) (T val) {
    char[] ret = new char[32];
    return cFloat.format (ret, val, T.dig+2, 1);
}
char[] parseFrom(T : real) (T val) {
    char[] ret = new char[32];
    return cFloat.format (ret, val, T.dig+2, 1);
}
debug (UnitTest) unittest {
    // NOTE: these numbers are not particularly meaningful.
    assert (parseFrom!(float) (0.0f) == "0.00000000");
    assert (parseFrom!(double) (-1e25) == "-1.00000000000000000e+25");
    assert (parseFrom!(real) (cast(real) 4.918e300) == "4.91800000000000000000e+300");
}
//END parrseFrom templates

//BEGIN Length templates
/* This template provides the initial length for strings for formatting various types. These strings
 * can be expanded; this value is intended to cover 90% of cases or so.
 *
 * NOTE: This template was intended to provide specialisations for different types.
 * This one value should do reasonably well for most types.
 */
private {
    template defLength(T)        { const uint defLength = 20; }
    template defLength(T : char) { const uint defLength = 4;  }
    template defLength(T : bool) { const uint defLength = 5;  }
}
//END Length templates

//BEGIN Utility funcs
private char[] formatLong (long val) {
    // May throw an IllegalArgumentException; don't bother catching and rethrowing:
    return cInt.toString (val);
}
private bool isEscapableChar (char c) {
    return ((c <= '\r' && c >= '\a') || c == '\"' || c == '\'' || c == '\\');
}
// Throws on unsupported escape sequences; however this should never actually happen within parseFrom.
private char replaceEscapableChar (char c) {
    // This code was generated:
    if (c <= '\v') {
        if (c <= '\b') {
            if (c == '\a') {
                return 'a';
            } else if (c == '\b') {
                return 'b';
            }
        } else {
            if (c == '\t') {
                return 't';
            } else if (c == '\n') {
                return 'n';
            } else if (c == '\v') {
                return 'v';
            }
        }
    } else {
        if (c <= '\r') {
            if (c == '\f') {
                return 'f';
            } else if (c == '\r') {
                return 'r';
            }
        } else {
            if (c == '\"') {
                return '\"';
            } else if (c == '\'') {
                return '\'';
            } else if (c == '\\') {
                return '\\';
            }
        }
    }
    
    // if we haven't returned:
    throw new IllegalArgumentException ("Character is not escapable (internal parseFrom error)");
}

debug (UnitTest) {
    import tango.io.Console;
    
    unittest {
        Cout ("Running unittest: parseFrom ...").flush;
        
        assert (parseFrom!(char[]) ("\a\b\t\n\v\f\r\"\'\\") == "\"\\a\\b\\t\\n\\v\\f\\r\\\"\\\'\\\\\"");
        
        Cout (" complete").newline;
    }
}
//END Utility funcs