From dcc37dbe5914b07daa722025fbe8dc00c78bc1dc Mon Sep 17 00:00:00 2001
From: Starbeamrainbowlabs <sbrl@starbeamrainbowlabs.com>
Date: Thu, 2 Jul 2020 16:25:54 +0100
Subject: [PATCH] Implement initial stream-slice subcommand

---
 src/Helpers/MathsHelpers.mjs           | 15 ++++++++
 src/Subcommands/stream-slice/index.mjs | 48 ++++++++++++++++++++++++++
 src/Subcommands/stream-slice/meta.toml | 25 ++++++++++++++
 3 files changed, 88 insertions(+)
 create mode 100644 src/Helpers/MathsHelpers.mjs
 create mode 100644 src/Subcommands/stream-slice/index.mjs
 create mode 100644 src/Subcommands/stream-slice/meta.toml

diff --git a/src/Helpers/MathsHelpers.mjs b/src/Helpers/MathsHelpers.mjs
new file mode 100644
index 0000000..8b9dd1d
--- /dev/null
+++ b/src/Helpers/MathsHelpers.mjs
@@ -0,0 +1,15 @@
+"use strict";
+
+/**
+ * Convenience function for calculating the percentage betwween 2 given values.
+ * @param	{Number}	count_so_far	The fractional part (e.g. items done so far)
+ * @param	{Number}	total			The total part (e.g. the total number of items to do)
+ * @param	{Number}	[range=100]		The range to transform to (default: 100)
+ * @return	{Number}	The calculated percentage.
+ */
+function percentage(count_so_far, total, range=100) {
+	if(count_so_far == 0) return 0;
+	return (count_so_far/total)*range;
+}
+
+export { percentage };
diff --git a/src/Subcommands/stream-slice/index.mjs b/src/Subcommands/stream-slice/index.mjs
new file mode 100644
index 0000000..ad409b4
--- /dev/null
+++ b/src/Subcommands/stream-slice/index.mjs
@@ -0,0 +1,48 @@
+"use strict";
+
+import fs from 'fs';
+
+import Terrain50 from 'terrain50';
+
+import a from '../../Helpers/Ansi.mjs';
+import l from '../../Helpers/Log.mjs';
+
+import { percentage } from '../../Helpers/MathsHelpers.mjs';
+
+export default async function(settings) {
+	// 1: Parse settings
+	let stream_in = process.stdin;
+	if(settings.cli.input !== "-") {
+		l.log(`Reading from ${a.hicol}${settings.cli.input}${a.reset}`);
+		stream_in = fs.createReadStream(settings.cli.input);
+	}
+	else
+		l.log(`Reading from stdin`);
+	
+	let stream_out = process.stdout; 
+	if(settings.cli.output !== "-") {
+		l.log(`Writing to ${a.hicol}${settings.cli.output}${a.reset}`);
+		stream_out = fs.createWriteStream(settings.cli.output);
+	}
+	else
+		l.log(`Writing to stdout`);
+	
+	let count = settings.cli.count,
+		offset = settings.cli.offset;
+	
+	// ------------------------------------------------------------------------
+	
+	let i = -1;
+	for await(let next of Terrain50.ParseStream(stream_in)) {
+		i++;
+		
+		if(i < offset) continue;
+		
+		let is_last = i - offset >= count;
+		await next.serialise(stream_out, is_last);
+		
+		let percentage = percentage(i - offset, count);
+		process.stderr.write(`Written ${i - offset} / count objects (~${count.toFixed(2)}%)       \r`);
+	}
+	l.log(`Slicing complete`);
+}
diff --git a/src/Subcommands/stream-slice/meta.toml b/src/Subcommands/stream-slice/meta.toml
new file mode 100644
index 0000000..7f0b7f3
--- /dev/null
+++ b/src/Subcommands/stream-slice/meta.toml
@@ -0,0 +1,25 @@
+description = "Extract a slice from a larger stream of objects"
+
+[[arguments]]
+name = "input"
+description = "The input file to extract a slice from (default: stdin)"
+default_value = "-"
+type = "string"
+
+[[arguments]]
+name = "output"
+description = "The output file to write to (default: stdout)"
+default_value = "-"
+type = "string"
+
+[[arguments]]
+name = "count"
+description = "The number of objects to extract (default: 1)"
+default_value = 1
+type = "integer"
+
+[[arguments]]
+name = "offset"
+description = "The number of objects to skip before beginning extraction (default: 0)"
+default_value = 0
+type = "integer"