/** Resource paths module.
*
* Internally to mde code other than code dealing directly with files and this module, paths are
* relative to the mde directory. This module transforms those paths to absolute paths.
*
* Additionally, the intention is to look for all files in two directories: the installation (i.e.
* main data) directory and a user directory (for user-specific configuration). Besides exposing
* both paths and checking in which valid files exist, this module provides some extra mergetag
* functionality to simplify correct reading and writing.
*
* Currently the paths are found as follows: (see codeDoc/paths.txt)
*/
/* Implementation note:
* All paths are stored internally as strings, rather than as an instance of FilePath/PathView once
* the FilePath has served its immediate purpose, since it's more convenient and creating new
* FilePaths for adjusted paths should be no slower than mutating existing ones. */
module mde.resource.paths;

import mde.exception;
import mde.mergetag.Reader;
import mde.mergetag.Writer;
import mde.mergetag.DataSet;
import mde.mergetag.exception;

import tango.io.FilePath;
import tango.util.log.Log : Log, Logger;
import tango.stdc.stdlib;
import tango.stdc.stringz;

/** Order to read files in.
*
* Values: HIGH_LOW, LOW_HIGH, HIGH_ONLY. */
enum PRIORITY : byte { HIGH_LOW, LOW_HIGH, HIGH_ONLY }

/** This struct has one instance for each "directory".
*
* It is the only item within this module that you should need to interact with. */
struct mdeDirectory
{
    /** Creates an MT reader for each file.
    *
    * Params:
    *   file      = The file path and name relative to the mdeDirectory, without a suffix
    *               (e.g. "options")
    *   readOrder = Read the highest priority or lowest priority files first? For correct merging,
    *               this should be LOW_HIGH when newly-read items override old ones (as is the case
    *               with DefaultData) and HIGH_LOW when the first-read items survive. Thus override
    *               order needs to be the same for each section, except the header which is always
    *               read with LOW_HIGH order.
    *               Alternately, for files which shouldn't be
    *               merged where only the highest priority file should be read, pass HIGH_ONLY.
    *   ds        = The dataset, as for mergetag. Note: all actual readers share one dataset.
    *   rdHeader  = Read the headers for each file and merge if rdHeader == true.
    */
    IReader makeMTReader (char[] file, PRIORITY readOrder, DataSet ds = null, bool rdHeader = false)
    {
        if (readOrder == PRIORITY.HIGH_ONLY) return makeReader (paths[pathsLen-1] ~ file, ds, rdHeader);
        else return new mdeReader (file, readOrder, ds, rdHeader, paths);
    }
    
    /** Creates an MT writer for file deciding on the best path to use.
    *
    * Params:
    *   file      = The file path and name relative to the mdeDirectory, without a suffix
    *               (e.g. "options")
    *   ds        = The dataset, as for mergetag.
    */
    IWriter makeMTWriter (char[] file, DataSet ds = null)
    {
        // FIXME: use highest priority writable path
        return makeWriter (paths[pathsLen-1] ~ file, ds, WriterMethod.Text);
    }
    
    /** Check whether the given file exists under any path with either .mtt or .mtb suffix. */
    bool exists (char[] file) {
        for (uint i = 0; i < pathsLen; ++i) {
            if (FilePath (paths[i]~file~".mtt").exists) return true;
            if (FilePath (paths[i]~file~".mtb").exists) return true;
        }
        return false;
    }
    
private:
    
    // Unconditionally add a path
    void addPath (char[] path) {
        paths[pathsLen++] = path~'/';
    }
    
    // Test a path and add if is a folder
    void tryPath (char[] path) {
        PathView pv = FilePath (path);
        if (pv.exists && pv.isFolder) {
            paths[pathsLen++] = path~'/';
            logger.info ("Path "~path~" is writable: " ~ (pv.isWritable ? "yes" : "no"));
        }
    }
    
    // Use a static array to store all possible paths with separate length counters.
    // Lowest priority paths are first.
    char[][MAX_PATHS] paths;
    ubyte pathsLen = 0;
}

/** These are the actual instances, one for each of the data and conf "directories". */
mdeDirectory dataDir, confDir;

//BEGIN Path resolution
static this() {
    logger = Log.getLogger ("mde.resource.paths");
    
    // NOTE: May fail. Currently I think I'll just let the exception halt execution.
    resolvePaths();
    if (!dataDir.pathsLen) throw new mdeException ("Fatal: no data path found!");
    if (!confDir.pathsLen) throw new mdeException ("Fatal: no conf path found!");
}

private:
// The maximum number of paths for any one "directory".
// There are NO CHECKS that this is not exceeded.
const MAX_PATHS = 3;

Logger logger;

/* Try each path in succession, returning the first two exist and be a folder. Throws if none are. */
char[] findPath (char[][] paths ...) {
    foreach (path; paths) {
        PathView pv = new FilePath (path);
        if (pv.exists && pv.isFolder) return pv.toString;    // got a valid path
    }
    // no valid path...
    logger.fatal ("Unable to resolve a required path! The following were tried:");
    foreach (path; paths) logger.fatal ('\t' ~ path);
    throw new mdeException ("Unable to resolve a required path (see log for details).");
}

// These are used several times:
const DATA = "/data";
const CONF = "/conf";

version (linux) {
    void resolvePaths () {
        // Home directory:
        char[] HOME = fromStringz (getenv (toStringz ("HOME")));
        
        // Base paths:
        char[] staticPath = findPath ("/usr/share/games/mde", "/usr/local/share/games/mde", "data");
        char[] userPath = findPath (HOME~"/.config/mde", HOME~"/.mde");
        
        // Static data paths:
        dataDir.addPath (staticPath);      // we know this is valid anyway
        dataDir.tryPath (userPath ~ DATA);
        
        // Configuration paths:
        confDir.tryPath (staticPath ~ CONF);
        confDir.tryPath ("/etc/mde");
        confDir.tryPath (userPath ~ CONF);
    }
} else version (Windows) {
    void resolvePaths () {
        static assert (false, "No registry code");
        
        // Base paths:
        char[] userPath = `...`;
        char[] installPath = `registryInstallPath or "."`;
        char[] staticPath = findPath (installPath ~ DATA);
        
        // Static data paths:
        dataDir.addPath[dataLength++] = staticPath;   // we know this is valid anyway
        dataDir.tryPath (userPath ~ DATA);
        
        // Configuration paths:
        confDir.tryPath (staticPath.toString ~ CONF);
        confDir.tryPath (installPath ~ CONF);
        confDir.tryPath (userPath.toString ~ CONF);
    }
} else {
    static assert (false, "Platform is not linux or Windows: no support for paths on this platform yet!");
}
//END Path resolution

/** A special adapter for reading from multiple mergetag files with the same relative path to an
* mdeDirectory simultaneously.
*/
class mdeReader : IReader
{
    private this (char[] file, PRIORITY readOrder, DataSet ds, bool rdHeader, char[][MAX_PATHS] paths)
    in { assert (readOrder == PRIORITY.LOW_HIGH || readOrder == PRIORITY.HIGH_LOW); }
    body {
        rdOrder = readOrder;
        if (ds is null) ds = new DataSet;
        
        foreach (path; paths) {
            try {
                IReader r = makeReader (path~file, ds, rdHeader);
                
                readers[readersLen++] = r;
            }
            catch (MTFileIOException) {}    // Ignore errors regarding no file for now.
        }
        
        if (readersLen == 0) {          // totally failed to find any valid files
            throw new MTFileIOException ("Unable to find the file: "~file[1..$]~"[.mtt|mtb]");
        }
        
        // This is simply the easiest way of adjusting the reading order:
        if (readOrder == PRIORITY.HIGH_LOW) readers[0..readersLen].reverse;
    }
    
    DataSet dataset () {                /// Get the DataSet
        return readers[0].dataset;      // all readers share the same dataset
    }
    void dataset (DataSet ds) {         /// Set the DataSet
        for (uint i = 0; i < readersLen; ++i) readers[i].dataset (ds);
    }
    
    void dataSecCreator (IDataSection delegate (ID) dsC) {  /// Set the dataSecCreator
        for (uint i = 0; i < readersLen; ++i) readers[i].dataSecCreator = dsC;
    }
    
    /** Get identifiers for all sections.
    *
    * Note: the identifiers from all sections in all files are just strung together, starting with
    * the highest-priority file. */
    ID[] getSectionNames () {
        ID[] names;
        for (int i = readersLen-1; i >= 0; --i) names ~= readers[i].getSectionNames;
        return names;
    }
    void read () {                      /// Commence reading
        for (uint i = 0; i < readersLen; ++i) readers[i].read();
    }
    void read (ID[] secSet) {           /// ditto
        for (uint i = 0; i < readersLen; ++i) readers[i].read(secSet);
    }
    void read (View!(ID) secSet) {      /// ditto
        for (uint i = 0; i < readersLen; ++i) readers[i].read(secSet);
    }
        
    private:
    IReader[MAX_PATHS] readers;
    ubyte readersLen = 0;
    
    PRIORITY rdOrder;
}