"use strict";

const matchValue = require("match-value");
const asExpression = require("as-expression");

const FIELD_MAPPINGS = {
	attrset_expression: {
		binding_set: "MERGE"
	},
	rec_attrset_expression: {
		binding_set: "MERGE"
	},
	let_attrset_expression: {
		binding_set: "MERGE"
	},
	let_expression: {
		binding_set: "MERGE"
	}
};

function mergeNode(parent, child) {
	// NOTE: Mutates parent!
	let { type, ... childArgs } = child;
	Object.assign(parent, childArgs);
}

// TODO: Refactor this
function convertStringNodeParts(node) {
	let fullText = node.text;
	let currentIndex = node.startIndex;
	let parts = [];

	function relative(index) {
		return index - node.startIndex;
	}

	for (let child of node.children) {
		if (child.type === "interpolation") {
			if (child.startIndex > currentIndex) {
				// We skipped some literal string
				let value = fullText.slice(relative(currentIndex), relative(child.startIndex));
				parts.push({ type: "NixInterpolationLiteral", value: value });
			}

			parts.push(convertNode(child));

			currentIndex = child.endIndex;
		}
	}

	if (currentIndex < node.endIndex) {
		// Last bit of string literal at the end
		let value = fullText.slice(relative(currentIndex), relative(node.endIndex));
		parts.push({ type: "NixInterpolationLiteral", value: value });
	}

	return parts.map((part, i) => {
		// FIXME: Verify that this logic is correct, and also holds up for actual interpolated strings
		let isLiteralString = (part.type === "NixInterpolationLiteral");

		if (isLiteralString) {
			let strippedString = part.value;

			if (i === 0 && isLiteralString) {
				// Strip prefix quote
				strippedString = strippedString.slice(1);
			}

			if (i === parts.length - 1 && isLiteralString) {
				// Strip suffix quote
				strippedString = strippedString.slice(0, -1);
			}

			return { ... part, value: strippedString };
		} else {
			return part;
		}
	});
}

function convertNode(node) {
	let { type } = node;

	let result = (node.isNamed)
		? { type: type }
		: { type: "token", text: node.text }

	if (node.fields != null) {
		// console.log({ node, fields: node.fields, children: node.children });
		for (let field of node.fields) {
			let children = node[field];
			let fieldName = field.replace(/Nodes?$/, "");

			result[fieldName] = asExpression(() => {
				if (children == null) {
					return null;
				} else if (Array.isArray(children)) {
					return children.map(convertNode);
				} else {
					return convertNode(children);
				}
			});
		}

		let nodeFieldMappings = FIELD_MAPPINGS[node.type];

		if (nodeFieldMappings != null) {
			node.children.forEach((child, i) => {
				let mapTo = nodeFieldMappings[child.type];

				if (mapTo === "MERGE") {
					// This means we should elide the child node, and merge it into the node we're currently processing; this is used to deal with non-hidden layers of indirection
					mergeNode(result, convertNode(child));
				} else if (mapTo != null) {
					// TODO: Support for multi-child fields?
					result[mapTo] = convertNode(child);
				}
			});
		}
	}

	// Special case: if we don't provide a Babel-compatible top-level Program entry, traversal will fail
	if (type === "source_code") {
		return {
			type: "Program",
			sourceType: "script",
			body: [ result.expression ]
		};
	}

	// Special case: this is just a wrapper for an identifier, and we don't really want to keep this wrapper
	if (type === "variable_expression") {
		return convertNode(node.nameNode);
	}

	// The below section is based on `alias` expressions throughout the grammar, and the rules in https://github.com/cstrahan/tree-sitter-nix/blob/83ee5993560bf15854c69b77d92e34456f8fb655/grammar.js#L53-L59
	if (type === "identifier" || type === "attr_identifier") {
		// FIXME: attr_identifier gone?
		result.name = node.text;
	} else if (type === "integer_expression" || type === "float_expression") {
		result.value = node.text;
	} else if (type === "string_expression") {
		result.parts = convertStringNodeParts(node);
	} else if (type === "path_expression" || type === "hpath_expression") {
		result.path = node.text;
	} else if (type === "spath_expression") {
		// Strip the < and >
		result.path = node.text.slice(1, -1);
	} else if (type === "uri_expression") {
		result.uri = node.text;
	}

	if (type === "binary_expression" || type === "unary_expression") {
		// Unpack the anonymous token
		result.operator = result.operator.text;
	}

	if (type === "rec_attrset_expression") {
		result.recursive = true;
	} else if (type === "attrset") {
		result.recursive = false;
	}

	// FIXME: Is this code still needed after the parser updates?
	if (type === "inherit") {
		// We're inheriting from scope here, so the source expression is explicitly not set
		result.expression = result.expression ?? null;
	} else if (type === "inherit_from") {
		// Already set
	}

	if (type === "list_expression") {
		// TODO: Can this sort of renaming be done more neatly?
		result.elements = result.element;
		delete result.element;
	}

	// console.log(result);

	result.type = matchValue(result.type, {
		source_code: "NixProgram",
		token: "NixAnonymousToken",
		path_expression: "NixPathLiteral",
		hpath_expression: "NixHomePathLiteral", /* FIXME: Do we have interpolation support here yet? */
		spath_expression: "NixEnvironmentPathLiteral",
		uri_expression: "NixURILiteral",
		integer_expression: "NixIntegerLiteral",
		float_expression: "NixFloatLiteral",
		string_expression: "NixStringLiteral",
		parenthesized_expression: "NixParenthesizedExpression",
		attrset_expression: "NixAttributeSet",
		rec_attrset_expression: "NixAttributeSet",
		binding_set: "NixAttributeSetBindings",
		let_expression: "NixLetIn",
		let_attrset_expression: "NixLetAttributeSet",
		identifier: "NixIdentifier",
		attr_identifier: "NixAttributeIdentifier", // FIXME: Gone?
		attrpath: "NixAttributePath",
		inherit: "NixInherit",
		inherit_from: "NixInherit",
		inherited_attrs: "NixInheritAttributes",
		attrs_inherited_from: "NixInheritAttributes", // FIXME: Gone?
		binding: "NixBinding",
		unary_expression: "NixUnaryOperation",
		binary_expression: "NixBinaryOperation",
		apply_expression: "NixFunctionCall",
		select_expression: "NixAttributeSelection",
		interpolation: "NixInterpolationExpression",
		list_expression: "NixListLiteral",
		with_expression: "NixWithExpression",
		if_expression: "NixConditional",
		// Function definitions
		function_expression: "NixFunctionDefinition",
		formals: "NixUnpackedAttributes",
		formal: "NixUnpackedAttribute",
		// _: (value) => value
		// FIXME: assert_expression? if_expression? unary_expression? has_attr_expression? apply_expression? indented_string_expression? binding_set?
	});

	return result;
}

/* Produces an AST that's roughly shape-compatible with ESTree so that Babel can deal with it */
module.exports = function prepareAST(tree) {
	return convertNode(tree.rootNode);
};