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// SPDX-License-Identifier: MPL-2.0
// (c) Hare authors <https://harelang.org>
use ascii;
use fmt;
use io;
use memio;
use strings;
export type literal = str;
export type variable = str;
export type instruction = (literal | variable);
export type template = []instruction;
// Parameters to execute with a template, a tuple of a variable name and a
// formattable object.
export type param = (str, fmt::formattable);
// The template string has an invalid format.
export type invalid = !void;
// Returns a human-friendly string for [[invalid]].
export fn strerror(err: invalid) str = "Template string has invalid format";
// Compiles a template string. The return value must be freed with [[finish]]
// after use.
export fn compile(input: str) (template | invalid | nomem) = {
let buf = memio::dynamic();
defer io::close(&buf)!;
let instrs: []instruction = [];
let ok = false;
defer if (!ok) finish(&instrs);
const iter = strings::iter(input);
for (let rn => strings::next(&iter)) {
if (rn == '$') {
match (strings::next(&iter)) {
case let next_rn: rune =>
if (next_rn == '$') {
memio::appendrune(&buf, rn)!;
} else {
strings::prev(&iter);
const lit = memio::string(&buf)!;
append(instrs, strings::dup(lit)?: literal)?;
memio::reset(&buf);
parse_variable(&instrs, &iter, &buf)?;
};
case =>
return invalid;
};
} else {
memio::appendrune(&buf, rn)!;
};
};
if (len(memio::string(&buf)!) != 0) {
const lit = memio::string(&buf)!;
append(instrs, strings::dup(lit)?: literal)?;
};
ok = true;
return instrs;
};
// Frees resources associated with a [[template]].
export fn finish(tmpl: *template) void = {
for (let instr .. *tmpl) {
match (instr) {
case let lit: literal =>
free(lit);
case let var: variable =>
free(var);
};
};
free(*tmpl);
};
// Executes a template, writing the output to the given [[io::handle]]. If the
// template calls for a parameter which is not provided, an assertion will be
// fired.
export fn execute(
tmpl: *template,
out: io::handle,
params: param...
) (size | io::error) = {
let z = 0z;
for (let instr .. *tmpl) {
match (instr) {
case let lit: literal =>
z += fmt::fprint(out, lit)?;
case let var: variable =>
const value = get_param(var, params...);
z += fmt::fprint(out, value)?;
};
};
return z;
};
fn get_param(name: str, params: param...) fmt::formattable = {
// TODO: Consider preparing a parameter map or something
for (let (var_name, obj) .. params) {
if (var_name == name) {
return obj;
};
};
fmt::errorfln("strings::template: required parameter ${} was not provided", name)!;
abort();
};
fn parse_variable(
instrs: *[]instruction,
iter: *strings::iterator,
buf: *memio::stream,
) (void | invalid | nomem) = {
let brace = false;
match (strings::next(iter)) {
case let rn: rune =>
if (rn == '{') {
brace = true;
} else {
strings::prev(iter);
};
case =>
return invalid;
};
for (true) {
const rn = match (strings::next(iter)) {
case let rn: rune =>
yield rn;
case =>
return invalid;
};
if (brace) {
if (rn == '{') {
return invalid;
} else if (rn != '}') {
memio::appendrune(buf, rn)!;
} else {
break;
};
} else {
if (ascii::isalnum(rn) || rn == '_') {
memio::appendrune(buf, rn)!;
} else {
strings::prev(iter);
break;
};
};
};
const var = memio::string(buf)!;
append(instrs, strings::dup(var)?: variable)?;
memio::reset(buf);
};
def test_input: str = `Dear ${recipient},
I am the crown prince of $country. Your brother, $brother, has recently passed
away in my country. I am writing to you to facilitate the transfer of his
foreign bank account balance of $$1,000,000 to you.`;
def test_output: str = `Dear Mrs. Johnson,
I am the crown prince of South Africa. Your brother, Elon Musk, has recently passed
away in my country. I am writing to you to facilitate the transfer of his
foreign bank account balance of $1,000,000 to you.`;
@test fn template() void = {
const tmpl = compile(test_input)!;
defer finish(&tmpl);
let buf = memio::dynamic();
defer io::close(&buf)!;
execute(&tmpl, &buf,
("recipient", "Mrs. Johnson"),
("country", "South Africa"),
("brother", "Elon Musk"),
)!;
assert(memio::string(&buf)! == test_output);
};
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