/*
 * Copyright (c) 2024 Jeremy Baxter.  All rights reserved.
 *
 * Boost Software License - Version 1.0 - August 17th, 2003
 *
 * Permission is hereby granted, free of charge, to any person or
 * organization obtaining a copy of the software and accompanying
 * documentation covered by this license (the "Software") to use,
 * reproduce, display, distribute, execute, and transmit the Software,
 * and to prepare derivative works of the Software, and to permit
 * third-parties to whom the Software is furnished to do so, all
 * subject to the following:
 *
 * The copyright notices in the Software and this entire statement,
 * including the above license grant, this restriction and the following
 * disclaimer, must be included in all copies of the Software, in whole or
 * in part, and all derivative works of the Software, unless such copies or
 * derivative works are solely in the form of machine-executable object
 * code generated by a source language processor.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, TITLE AND
 * NON-INFRINGEMENT. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR ANYONE
 * DISTRIBUTING THE SOFTWARE BE LIABLE FOR ANY DAMAGES OR OTHER LIABILITY,
 * WHETHER IN CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/++
 + INI is a simple, concise configuration or data interchange
 + format. It consists of keys and values listed inside a section.
 + An INI document might look something like this:
 + ---
 + [user]
 + name = Kevin
 + age = 26
 + emailAddress = kevin@example.net
 +
 + [config]
 + useBundledMalloc = false
 + forceDefaultInit = true
 + ---
 +
 + $(B initial) is a library for parsing INI documents into an `INIUnit`,
 + a data structure representing an INI document. The function `readINI`
 + contains the parser; it parses the INI given to it and deserialises
 + it into the given `INIUnit`. The `readINIFile` function can be used
 + to read the INI from a file rather than a string.
 +
 + $(B initial) is fully @safe, and can be used in @safe code.
 +
 + License: [Boost License 1.0](https://www.boost.org/LICENSE_1_0.txt).
 + Authors: Jeremy Baxter
 +/
module initial;

import std.conv      : to, ConvException;
import std.exception : basicExceptionCtors, enforce;
import std.format    : format;
import std.traits    : isSomeChar;

private alias parserEnforce = enforce!INIParseException;

@safe:

/++
 + Structure that represents an INI file.
 +
 + Contains `INISection`s in an associative array that can be
 + directly accessed if needs be, or the index operator can be
 + used to get an `INISection` and automatically initialise it
 + if needed.
 +
 + The `serialise` method can be used to serialise the entire
 + structure into an INI document that can be then read again
 + by the parser and modified by humans.
 +
 + Example:
 + ---
 + INIUnit ini;
 +
 + /* write INI data */
 + ini["section"]["key"] = "value";
 + ini["section"]["num"] = "4.8";
 +
 + /* read INI data */
 + readINI(ini, `
 +     [section]
 +     num = 5.3
 + `);
 +
 + /* read INI from file */
 + readINIFile(ini, "config.ini");
 +
 + /* write INI to file */
 + import std.file : write;
 + write("config.ini", ini.serialise());
 + ---
 +/
struct INIUnit
{
	INISection[string] sections;     /++ Hashmap of INISections in this unit. +/
	string defaultSection = "main";  /++ Name of the default section. +/

	nothrow:

	/++
	 + Returns the value of *k* in the default section
	 + or *defaultValue* if *k* is not present.
	 +/
	string
	key(string k, string defaultValue = null)
	{
		return this[defaultSection].key(k, defaultValue);
	}

	/++
	 + Serialises this `INIUnit` into an INI document.
	 +
	 + If *defaultSectionHeading* is true, includes the
	 + section heading of the default section.
	 + Example:
	 + ---
	 + INIUnit ini;
	 +
	 + ini["sections"] = "ages suburbs";
	 + ini["ages"]["John"] = "37";
	 + ini["ages"]["Mary"] = "29";
	 + ini["suburbs"]["John"] = "Gordonton";
	 + ini["suburbs"]["Mary"] = "Ashmore";
	 +
	 + writeln(ini.serialise());
	 + /*
	 +  * sections = ages suburbs
	 +  * [ages]
	 +  * John = 37
	 +  * Mary = 29
	 +  * [suburbs]
	 +  * John = Gordonton
	 +  * Mary = Ashmore
	 +  */
	 + ---
	 +/
	char[]
	serialise(bool defaultSectionHeading = false)
	{
		char[] buf;

		buf = this[defaultSection].serialise(defaultSectionHeading);
		foreach (string sect; sections.byKey()) {
			if (sect == defaultSection)
				continue;

			buf ~= this[sect].serialise();
		}

		return buf;
	}

	/++
	 + Returns the `INISection` associated with the name *sect*.
	 + Initialises it if it doesn't exist.
	 +/
	ref INISection
	opIndex(string sect)
	{
		if (!(sect in sections))
			sections[sect] = INISection(sect);

		return sections[sect];
	}

	/++
	 + Sets the value of the key *k* in the default section to *v*.
	 + Example:
	 + ---
	 + ini["key"] = "value";
	 + ---
	 +/
	void
	opIndexAssign(string v, string k)
	{
		sections[defaultSection][k] = v;
	}

	/++
	 + Sets the value of the `INISection` named *sect*.
	 +/
	void
	opIndexAssign(INISection v, string sect)
	{
		sections[sect] = v;
	}
}

/++
 + Represents an INI section.
 +
 + Holds keys in the form of an associative array.
 + Index the `keys` property to get this data raw, or to avoid
 + range errors, use the `key` or `keyAs` functions.
 +
 + `alias this` is applied to the `keys` associative array,
 + meaning you can index the structure to get or set keys' values.
 +/
struct INISection
{
	string[string] keys;  /++ Hashmap of keys belonging to this section. +/
	string name;          /++ Name of this section. +/

	/++
	 + Construct a new `INISection` with the given name.
	 + Called by `readINI` and `INIUnit.opIndex`.
	 +/
	this(string name) nothrow
	{
		this.name = name;
	}

	/++
	 + Returns the value of `k` in this section or
	 + `defaultValue` if the key is not present.
	 +/
	string
	key(string k, string defaultValue = null) nothrow
	{
		return k in keys ? keys[k] : defaultValue;
	}

	/++
	 + Using `std.conv`, converts the value of *k* to *T*.
	 + On conversion failure throws an `INITypeException`
	 + with a message containing location information.
	 +/
	T
	keyAs(T)(string k, T defaultValue)
	{
		try
			return k in keys ? keys[k].to!T() : defaultValue;
		catch (ConvException)
			throw new INITypeException(
				format!"unable to convert [%s].%s to %s"(name, k, T.stringof));
	}

	/++
	 + Serialise this section into an INI document.
	 +
	 + If `sectionHeading` is true, includes the section heading at the top.
	 +/
	char[]
	serialise(bool sectionHeading = true) nothrow
	{
		char[] buf;

		if (sectionHeading)
			buf ~= "[" ~ name.to!(char[]) ~ "]\n";

		foreach (string key; keys.byKey()) {
			buf ~= key ~ " = " ~ keys[key] ~ "\n";
		}

		return buf;
	}

	alias keys this;
}

/++
 + Exception thrown when parsing failure occurs.
 +/
class INIParseException : Exception
{
	mixin basicExceptionCtors;
}

/++
 + Exception thrown when conversion failure occurs.
 +/
class INITypeException : Exception
{
	mixin basicExceptionCtors;
}

private string
locate(size_t l, size_t c)
{
	return format!"%d:%d"(l, c);
}

/++
 + Parse the given INI data into an `INIUnit`.
 +
 + To parse a file's contents, use readINIFile instead.
 +
 + Whitespace is first stripped from the beginning and end of
 + the line before parsing it.
 +
 + The following rules apply when parsing:
 + $(UL
 + $(LI if a hash character `#` is found at the beginning of a line,
 +      the rest of the line is ignored)
 + $(LI if a left square bracket character `[` is found at
 +      the beginning of a line, the line is considered a
 +      section heading)
 + $(LI inside a section heading, any character can be used
 +      inside the section heading except the right square bracket
 +      character)
 + $(LI once the right square bracket character `]` is found,
 +      the section heading is considered finished. Any trailing
 +      characters are garbage and will trigger a parse error.)
 + $(LI if a character except the left square bracket is found
 +      at the beginning of a line, the line is considered an
 +      assignment in the current section)
 + $(LI once an equals character `=` is found after the first
 +      part of an assignment, the rest of the line is considered
 +      the "value" while the first part is the "key")
 + $(LI if whitespace is found in the first part of an assignment,
 +      it is ignored and the next equals sign is looked for
 +      immediately)
 + $(LI if whitespace is found after an equals character `=`
 +      in an assignment, it is ignored until the first
 +      non-whitespace character is found)
 + $(LI once a non-whitespace character is found after an equals
 +      character `=` in an assignment, it is counted part of the
 +      "value")
 +/
void
readINI(ref INIUnit ini, string data)
{
	import std.string : splitLines, strip;

	string section;  /* name of current section */
	string text;     /* current key, value, section, whatever */
	string key;      /* name of key in section */
	string value;    /* value */
	bool inAssign;   /* in key assignment? */
	bool inHeading;  /* in section heading? */
	bool needEqls;   /* require equals sign immediately? */
	bool pastEqls;   /* past equals sign in assignment? */
	bool trailing;   /* trailing garbage after heading? */

	section = ini.defaultSection;

	nextline:
	foreach (size_t ln, string line; data.splitLines()) {
		line = line.strip();
		if (line.length == 0)
			continue;

		inAssign = inHeading = needEqls = pastEqls = trailing = false;
		text = key = value = "";
		foreach (size_t cn, char ch; line) {
			switch (ch) {
			/* comment? */
			case '#':
				if (cn == 0)
					continue nextline;

				text ~= ch;
				break;

			/* beginning of a section heading? */
			case '[':
				if (cn == 0) /* beginning of line? */
					inHeading = true;
				else
					text ~= ch;
				break;

			/* end of a section heading? */
			case ']':
				parserEnforce(inHeading || inAssign,
					locate(ln, cn) ~ ": unexpected character ']'");

				if (inHeading) {
					section = text;
					text = "";
					inHeading = false;
					trailing = true;
				} else if (inAssign) {
					text ~= ch;
				}
				break;

			/* middle of an assignment? */
			case '=':
				if (inAssign) {
					if (pastEqls) {
						/* count it as part of the value */
						text ~= ch;
					} else {
						key = text;
						text = "";
						pastEqls = true;
						needEqls = false;
					}
				} else {
					goto default;
				}
				break;

			/* whitespace */
			case ' ':
			case '\t':
			case '\v':
			case '\r':
			case '\n':
			case '\f':
				if (inAssign) {
					if (!pastEqls)
						needEqls = true;
				}
				break;

			default:
				if (cn == 0) /* beginning of line? */
					inAssign = true;

				parserEnforce((inAssign || inHeading) && !trailing,
					locate(ln, cn) ~ ": unexpected character '" ~ ch ~ "'");

				if (inAssign)
					parserEnforce(!needEqls,
						locate(ln, cn) ~ ": expected '=', not '" ~ ch ~ "'");

				text ~= ch;
				break;
			}
		}
		/* once the line has finished being looped over... */
		if (inAssign) {
			parserEnforce(key.length != 0,
				locate(ln, line.length - 1) ~ ": key cannot be empty");
			value = text;
			text = "";

			if (!(section in ini.sections))
				ini[section] = INISection(section);
			ini[section][key] = value;
		}
	}
}

/++
 + Parse INI from a file located at `fileName`.
 +/
void
readINIFile(ref INIUnit ini, string fileName)
{
	import std.file : readText;

	readINI(ini, readText(fileName));
}